1. Field
Example embodiments relate to a semiconductor device including polysilicon (poly-Si). Other example embodiments relate to a semiconductor device which includes a conductive material layer that induces more stable growth of poly-Si and/or reduces diffusion into poly-Si when poly-Si used in forming a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
Polysilicon (poly-Si) is a material that is widely used in the art to form a semiconductor device (e.g., a diode or a thin film transistor (TFT)). Poly-Si may be deposited at a low temperature and may be doped at a substantially high concentration. Cross-point type memory devices having a diode (1 D)-resistor (1 R) structure are acknowledged in the art. Poly-Si may be used for a silicon diode (e.g., a p-n type or schottky barrier diode).
FIG. 1 is a diagram illustrating a perspective view of a conventional p-n junction diode.
Referring to FIG. 1, a p-type poly silicon (Si) layer 12 and an n-type poly-Si layer 13 may be formed on a lower electrode 11. The p-type poly-Si layer 12 and the n-type poly-Si layer 13 may form a diode structure. An upper electrode 14 may be formed on the p-type poly-Si layer 12 and the n-type poly-Si layer 13. In a cross-point type memory device, for example, of a resistive random access memory (RRAM), the lower electrode 11 and the upper electrode 14 cross each other and a storage node formed may be formed between the diode structure and the upper electrode 14. The storage node may be formed of a transition metal oxide.
It may be desirable to form electrodes, which have increased adhesion characteristics with respect to silicon, below poly-Si. The crystallinity of poly-Si grown on the electrodes may be high. A material that deters diffusion from the electrodes into poly-Si may be desirable.
In the conventional art, tungsten (W), tantalum (Ta) and/or titanium (Ti) are used to form electrodes below poly-Si. The conventional art acknowledges a method of preventing metal diffusion by forming a barrier layer (e.g., TiN or the like) between a lower electrode and poly-Si. Because the above-mentioned metals do not exhibit the desired adhesion characteristics with respect to silicon, it may be difficult to form higher-quality poly-Si during excimer laser annealing (ELA). A substantial amount of diffusion may occur from the metal into poly-Si during an ELA or any subsequent annealing process(es), making it difficult to form a p-n diode.
FIG. 2A is a graph illustrating the results of secondary ion mass spectroscopy (SIMS) of a conventional poly-Si/Ti/Mo/SiO2 sample that is crystallized by ELA at a low temperature.
In FIG. 2A, molybdenum (Mo) and titanium (Ti) were used to form a metallic layer on a SiO2 insulating thin film. A low temperature annealing process was performed on a sample in order to apply silicon on the metallic layer, forming poly-Si. The composition value per ingredient was determined based on the depth of the sample.
Referring to FIG. 2A, Ti and Mo were observed in a short sputtering time. As such, the materials used to form the Ti and Mo layers below a poly-Si layer diffuse and penetrate into poly-Si during the ELA process.
FIG. 2B shows a transmission electron microscope (TEM) image taken long a cross-section of a conventional poly-Si/Ti/Mo/SiO2 sample crystallized by ELA.
Referring to FIG. 2B, a region representing the formation of silicide (e.g., Si—Ti or Si—Mo) from the reaction of Si and Ti (and Mo when the Si is changed into a liquefied state during an ELA process) is present. Silicide reduces (or lowers) the melting point of the metal. As such, the metal diffuses into the silicon layer. According to example embodiments, the metal may diffuse into the surface of poly-Si through a grain boundary of poly-Si. As such, the device may not exhibit the desired characteristics.
FIG. 3A is a microscopic photo showing the surface of a conventional amorphous-Si/Ti/Mo/Ti/SiO2(a-Si/Ti/Mo/Ti/SiO2) sample after annealing. The a-Si/Ti/Mo/Ti/SiO2 sample in FIG. 3A was annealed for about 5 minutes in an N2 atmosphere of about 500° C.
FIG. 3B is a microscopic photo showing the surface of a conventional a-Si/Ti/W/Ti/SiO2 sample after annealing. The a-Si/Ti/W/Ti/SiO2 sample in FIG. 3B was annealed for about 5 minutes in an N2 atmosphere of about 500° C.
Referring to FIGS. 3A and 3B, if the a-Si/Ti/Mo/Ti/SiO2 sample and the a-Si/Ti/W/Ti/SiO2 sample are annealed in an N2 atmosphere of about 500° C., a-Si forms silicide due to an increased reaction property with a lower metallic layer. As such, the surface of the thin film becomes rough.